Alpha Numeric sort in sql

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SQL-Server-2008R2

Hi i am currently doing a project in which the database needs to sort the lot numbers
prefix is nvarchar
lotnum is int
suffix is nvarchar

i have managed to convert the lot number
code i used is

Select (case when prefix is null then '' else prefix end) +
CONVERT ( nvarchar , ( lotnumber ) ) +(case when suffix is null then '' else suffix end)

(values in the database are a1a,1a,1,2,100)
when i order by lotnumber i get

a1a
1a
1
2
100

then prefix to the order by
and get this result

1
a1a
1a
2
100

i have added the suffix as well and returns the same result

i need to order it as follows

1
1a
2
100
a1a

Please could someone help me on this